1. Field of the Invention
The present invention relates to a method of recycling used wooden railroad ties and to the resultant structure of the recycled wooden ties.
2. Description of the Prior Art
Hardwood railroad ties are originally produced by traditional sawmill methods, i.e., cutting trees into the proper rectangular shape using rip saws and cross-cut saws. A rip saw is a saw used to cut wood in a direction generally parallel to the grain of the wood. Similarly, cross-cutting is the cutting of wood in a direction generally perpendicular to the grain of the wood. The trees are usually cut in such a manner that the grain of the tree is generally parallel to the longitudinal direction of the tie. The properly cut pieces are then coated with a preservative such as creosote and baked under heat and pressure to force the preservative into the wood fibers.
After installation into the track, the ties begin to degrade because of exposure to the weather, such as sunlight, particularly ultraviolet radiation, and because of physical forces exerted upon the ties by the trains. Eventually, the tie will "wear out" and need to be replaced. Railroad maintenance personnel routinely inspect ties when they are performing maintenance on the tracks. If they feel that a tie is excessively split or cannot properly hold spikes any longer, the tie is removed from the tracks and replaced with a new one.
The method of cutting trees to construct railroad ties has some disadvantages. It is not a cost-effective method, especially in view of the recent price increase of raw wood. Another disadvantage in utilizing a tree is that it leaves a lot of waste wood. Further, from an environmental viewpoint, it depletes an already depleted hardwood resource.
There have been numerous inventions related to various ways to construct wooden railroad ties from new and smaller wooden pieces. For example, U.S. Pat. No. 4,105,159 discloses a method of constructing wooden railroad ties from wooden plates and particle boards. U.S. Pat. No. 4,326,669 also discusses a use of unused wooden pieces disposed in different directions to form a railroad tie so as to maximize the mechanical strength of the tie utilizing the dependence of properties of wood pieces on grain directions.
The methods used to construct railroad ties disclosed in the references mentioned above utilize smaller pieces of wood than a railroad tie. These methods may, therefore, make use of wood in smaller than tie-size pieces. However, they do not eliminate the need for new pieces of wood which are costly and which has the other disadvantages previously discussed.
The other end of the spectrum in conserving wood is the use of artificial materials to construct railroad ties. Artificial ties made from concrete and other materials last longer than hardwood ties, but are not widely used by railroad companies because they require special handling and fastening procedures and are also considerably more expensive.
There has been an attempt to recycle used hardwood ties by grinding the used railroad ties into chips and mixing the chips with a phenolic resin and then molding the mixture into new ties using heat and pressure. The product was not a commercial success primarily because the finished product resembled artificial ties too closely in cost and performance.
Therefore, a need remains for a way to manufacture new railroad ties from recycled wooden ties in a cost-effective manner.
It is an object of the present invention to provide a method to recycle used railroad ties.